Divide the stitch number for the base of the mitten in half, then center your cable based on number of stitches in that half. Just be sure and put the cable on different sides for left and right

For example. If you had 48 stitches, and you want to do a 10 stitch braided cable, you would take 24 stitches, subtract 10 and have 14 left. Knit in 7 stitches, do the 10 stitch braided cable pattern, then knit 31 (the remaining 7 on that half of the mitten plus the 24 on the other half.)

When you do the other hand, knit 31, do your cable, knit 7

Since your cable pattern is established at the base of the hand in most cases, you will just keep the cable in the same place as the thumb stitches are seperated and with any decrease or increases. You don't need to refigure.

If your cable pattern is more or less stitches, adjust accordingly.

If you want your ribbed cuff to go into the cable, start your rib so that , in the case of a 48 stitch cast on, for example, you would be purling on stitch 8 to match the 10 stitch cable pattern. Adjust accordingly for other numbers of stitches.

The 10 stitch braided cable I like is a basic 6 row pattern.

Do about six rows at the top of the ribbing where you simply p2, k6, p2 where you want your cable placed.